Sinking porch slab

Reply

  #1  
Old 07-30-07, 08:29 PM
Member
Thread Starter
Join Date: Jul 2007
Posts: 3
Received 0 Votes on 0 Posts
Unhappy Sinking porch slab

I need help! I have a covered porch (no railings) with 4 colums that is sinking on one side. 2 of the colums are just hanging from the top and the other 2 are trying to lift as the slab sinks on one side. The porch is original with the home construction and has never had problems for over 20 years. Then it started sinking a little toward the house and now the problem just gets worse after each rain with more water running toward the house and it sinks a little more. I have had it slab-jacked TWICE! The second time he said there was no way it was going to sink now. Well, it still is.

After the second slab-jacking it could not be pushed any higher due to something holding it from going up any farther, so it still had a slight slope to the house for the rain water to run toward the house. There was about 18" of fly-ash and cement pumped under the whole porch.

With that much material under the slab, if I were to brick paver the porch with a slope away from the home, should this fix the sinking problem by stopping the water getting back under there? I get no movement during the dry drought we have been in, but once the rains come, I can see the pencil marks get longer. It has sunk about 1.5" so far. The colum pressure has to be great because the roof lines are still straight and the slab is just under a slight bow. It's hard to see the bow, but when the water comes, it's quite clear how it now lays.

I would like to thank EVERYONE in advance for all responses to help me fix this problem.
 
Sponsored Links
  #2  
Old 07-31-07, 06:43 AM
Member
Join Date: Apr 2007
Location: Canada
Posts: 415
Received 0 Votes on 0 Posts
Sounds to me that your problem is with the soil beneath the house. Trying to repair the symptoms will not likely make the problem disappear, as you have already discovered.

My suggestion, since I can't see the site, is for you to hire a local soils engineering firm to assess what the problem is and recommend how to correct it once and for all, rather than leaving it to contractors who either don't understand the problem or see you as their next repeat customer.

Brick pavers (interlocking bricks) will not resolve the problem because they allow water to go into the soil underneath them through the joints. A solid concrete or asphalt surface is impervious and with the right slope can alleviate the problem (or possibly correct it altogether) unless rain water can still seep to the trouble spot through the granular material underneath the impervious area.
 
  #3  
Old 07-31-07, 08:18 AM
Member
Thread Starter
Join Date: Jul 2007
Posts: 3
Received 0 Votes on 0 Posts
Thanks for the reply. I was thinking about keeping the slab and using the brick pavers as a new surface to get the pitch away from the house. When I get the pitch, the water will not run back toward the house. They charge over $1000 each time for the slab-jacking (only 2 companies here) and I used both once and each one failed. Neither were able to jack the slab high enough to give the slab a pitch away from the home. I figure I would use the slab as the base and brick over top to get the pitch. I do not have the money for a tear-out and new slab and figure I can just spend that grand on brick pavers to get a pitch.

I just don't know if it is my best option (figuring money problems) to get this problem under control.

I have a full poured wall basement. My guess was that the construction company did not back fill right or well and that is why my slab sinks when water gets back there. Do you still think I need to hire a soil engineer? THANKS!
 

Last edited by 1shooter; 07-31-07 at 08:22 AM. Reason: soil engineer
  #4  
Old 07-31-07, 09:43 AM
Join Date: Mar 2005
Location: USA
Posts: 6,130
Received 0 Votes on 0 Posts
Sinking porch slab

If you think you have a soil backfill problem, you have to choices:

1. Call a soils or geotechnical engineer

or

2. Do it yourself and tear out the slab, excavate the soil you think is bad and backfill with good soil and make sure it is compacted.

Putting down pavers does not solve the problem, but only changes the slope temporarily until there is more settlement.

Clay pavers will be difficult to install properly. Trying to correct a 1 1/2" slope will take a lot of mortar.

You will not be able to put down the interlocking concrete concrete because the the base must be level and covered with a 1" sand setting bed. You cannot use the sand setting bed for leveling purposes.
 
  #5  
Old 08-01-07, 07:05 AM
Member
Join Date: Apr 2007
Location: Canada
Posts: 415
Received 0 Votes on 0 Posts
Here is my thinking. A house that is 20 years old has had plenty of time for normal settlement from such things as rain, snow load, etc. If the settlement continues, than my suspicion is that something abnormal is causing the symptom. The problem could well be more difficult to figure out than you may think, and that's why I think the time is right to call professional help in the form of a good soils engineer.

I am a civil engineer myself (not geotechnical though) and have seen many unusual soil conditions like a quick condition (like quicksand) under a freight railroad track, a highrise building built on top of an acquifer that kept sinking over many years, a subdivision built on a former landfill site, etc. Abnormal conditions call for special knowledge skills, not your average run of the mill treatment.

Without finding the root cause of the problem and solving that, the symptoms will likely persist and give you nightmares and an ongoing cost. It's better to nip it in the bud and sleep peacefully afterwards. Changing the pitch of the surface may help temporarily but I doubt it'll give you a lasting solution because the water will seep back into the trouble spot and the symptoms will re-surface, if not before, then at the next extended period of continuous rain when the soil completely saturates with water. The solution may not even be to remove/reinforce the soil but provide some sort of drain to keep the water from doing the damage. If the problem is caused by water, changing/reinforcing the soil may not do a thing!

Good luck
 
  #6  
Old 08-01-07, 08:46 AM
Member
Thread Starter
Join Date: Jul 2007
Posts: 3
Received 0 Votes on 0 Posts
I guess that a tear-out and a new slab is in my future. I sure hope I do not get a new slab and IT starts sinking too. But knowing my luck, that may just happen.

Thanks for the advice!
 
  #7  
Old 08-01-07, 11:06 AM
Member
Join Date: Apr 2007
Location: Canada
Posts: 415
Received 0 Votes on 0 Posts
Originally Posted by 1shooter View Post
I guess that a tear-out and a new slab is in my future. I sure hope I do not get a new slab and IT starts sinking too. But knowing my luck, that may just happen.

Thanks for the advice!
If you tear everything out, make sure to have the soil tested for subsurface water problems if anything about it looks suspicious once exposed, like excessive dampness, soft spots, etc.

One other possibility that comes to mind is buried decomposing organic trash. As the trash decomposes it gives off methane and settles. This can go on for a long time, but can also easily be removed if you expose it.
 
  #8  
Old 08-01-07, 04:27 PM
Member
Join Date: Feb 2005
Location: USA
Posts: 1,396
Received 0 Votes on 0 Posts
I had a job once where a set of steps kept sinking and sloping back toward the house. After mudjacking didn't work, we tore it out, bolted an angle iron to the foundation, and used the top of the angle iron as the bottom of the concrete. In other words the concrete sat on top of the angle iron against the house. We used rebar in the slab to tie everything together. That way, even if the backfill cntinued to settle, the slab would stay put.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description: